1. Field of the Invention
The invention is directed to a stator for a hydrodynamic torque converter, and in particular a stator produced by an injection molding process using axially drawn dies. The stator has a hub having blades provided thereon.
2. Description of the Relation Art
German reference DE 195 33 151 A1 discloses a stator for a hydrodynamic torque converter, the stator being arranged axially between a pump wheel and a turbine wheel. The stator carries stator blades by means of which hydraulic fluid flowing from the turbine wheel can be directed to the pump wheel at a desired angle.
A stator of the type mentioned above can be produced in various ways. For reasons of economy, an injection molding process with axially drawn tools or dies is preferred, wherein the dies have fill spaces in which material is introduced by means of the injection molding process. After the material solidifies, the dies are drawn apart axially and, in so doing, release the guide wheel. Aluminum is usually used as the material for an injection molding process of this kind. Disadvantageously however the low viscosity or fluidity of the aluminum material in the heated state allows material to exit from a contacting zone between the two dies, resulting in unwanted attachments or accretions to form at the stator blades. In order to remove these accretions, a chisel is inserted in the axial direction between a respective flow outlet of the stator blade and a flow inlet of a next stator blade. When cutting off the accretions, forces act on the inserted chisel which lead to expected breaking of the chisel, especially if the cutting edge of the chisel is very narrow in the circumferential direction. In view of this breakage, the cutting edge of the chisel of this kind usually has a width of at least 4 mm. But, as a detrimental consequence of this, there is formed an offset in the circumferential direction between the flow outlet of the stator blade and the flow inlet of the next guide wheel blade, such that the offset exceeds the 4-mm width required for the chisel. As a result, the guide length of the stator blade for the flow passing through it is shortened, which leads to poorer efficiency and poorer characteristics, adversely reducing torque multiplication of the converter.
Because of these disadvantages, stators are often produced from duroplastic, wherein duroplastic powder is introduced into a press mold and agglomerated or baked through heat and pressure to form a stator. While this produces a stator having a smooth surface, the surface cannot be subjected to subsequent cutting machining. Due to the required admixture of glass fibers and carbon fibers, machining of the surface forms cracks which coarsen the running surface of the material when making contact with another material such as steel. This results in considerable wear.
In the production process using duroplastic, it is not possible to connect an outer ring of a freewheel receiving the stator with the stator hub by means of an intermediary material engagement. It is likewise disadvantageous to press in the outer ring of the freewheel subsequently because the stator would crack in the region of its hub due to the brittleness of the duroplastic. Therefore, projections are provided at the inner diameter of the stator hub so as to positively engage grooves at the outer ring of the freewheel. However, cracks which lead to breakage form at these projections, especially as a result of sudden loading.
Duroplastic stators of the kind mentioned above are preferably drawn radially. While an optimum shape of the stator blades can be produced in this way, this production process is very expensive because a quantity of tools, corresponding to the quantity of guide wheel blades, is needed to remove the accretions formed on the outside of the stator blades after the duroplastic powder is agglomerated.